A number of vascular diagnostic and interventional medical procedures are now performed translumenally. For example, catheter is introduced to the vascular system at a convenient access location and guided through the vascular system to a target location using established techniques. Such procedures require vascular access, which is usually established during the well-known Seldinger technique. Vascular access is generally provided through an introducer sheath, which is positioned to extend from outside the patient body, through a puncture in the femoral artery for example, and into the vascular lumen. Catheters or other medical devices are advanced into the patient's vasculature through the introducer sheath, and procedures such as balloon angioplasty, stent placement, etc. are performed.
In particular, stents and stent delivery assemblies are utilized in a number of medical procedures and situations, and as such their structure and function are well known. A stent is a generally cylindrical prosthesis introduced via a catheter into a lumen of a body vessel in a configuration having a generally reduced diameter for transport and delivery, and then expanded to a diameter of the target vessel when deployed. In its expanded configuration, the stent supports and reinforces the vessel walls while maintaining the vessel in an open, unobstructed condition.
Balloon expandable stents are well known and widely available in a variety of designs and configurations. Balloon expandable stents are crimped to their reduced diameter about the delivery catheter, then maneuvered to the deployment site and expanded to the vessel diameter by fluid inflation of a balloon positioned between the stent and the delivery catheter. One example of a stent is described in US Patent Application having Publication No. 2004/0093073, published May 13, 2004, the content of which is incorporated herein by reference.
During advancement of the stent through a body vessel to a deployment site, the crimped stent must capable of securely maintaining its axial position on the delivery catheter. That is, the crimped stent must not translocate proximally or distally during advancement, and especially must not dislodge from the catheter. Stents that are not properly crimped, secured or retained to the delivery catheter may slip and will either be lost, be deployed in the wrong location or only be partially deployed. Moreover, the stent must be crimped in such a way as to minimize or prevent distortion of the stent, and thereby, minimize or prevent abrasion and/or trauma to the vessel walls. Additionally, if a stent has been coated with a beneficial agent, care must be taken when crimping the stent onto the delivery device that the coating is not disturbed or removed from the stent during the crimping process.
In the past, crimping has been performed by hand, often resulting in an undesirable application of uneven radial crimping forces to the stent. Such a stent must either be discarded or re-crimped. Stents that have been crimped multiple times can suffer from fatigue and may be scored or otherwise marked which can cause thrombosis. In fact, a poorly crimped stent can also damage the underlying balloon.
In addition to hand crimping of stents, automated crimping machines have been developed, wherein the automated crimping machines provide a more consistent crimp radial force during the crimping process or consistent profile. In addition to providing consistent crimping forces, many other crimping parameters can be closely controlled through the use of computer controls or mechanical controls. An example of such an automated crimping machine and related crimping methods can be seen in U.S. Pat. No. 6,629,350 to Motsenbocker. The crimping machine shown and described in the '350 patent includes a crimp head comprising a plurality of segments, wherein one end of each of the segments is constrained to rotate about a pin wherein the other end of the segments is allowed to translate about a second pin. In this arrangement, the translation of the second end of each of the segments controls the size of the opening formed by the distal ends of the segments. A shortcoming of such a design is wear of each of the segments at the pins. The increased wear increases the tolerances through which the crimp head can be operated, eventually the crimp head can no longer be held to a desired tolerance and therefore must be rebuilt. Thus there is a need for an improved crimp head design that can be held to tighter tolerances for a significant period of operation.
In addition to the balloon expandable stents described above, it would be desirable to provide a stent crimping system capable of loading (i.e., crimping) self-expanding stents into a delivery device, wherein the stent can be chilled during compression. Further still, once compressed into a delivery diameter, the crimped stent must then be inserted into a distal end of a delivery system while maintaining the delivery profile. In order to accomplish this, the crimping head must be constructed such that minimal friction exists between the stent and the head. Additionally, the delivery device must be retained relative to the crimping head and then advanced a known distance to insert the crimped stent, without damaging the delivery device.